1. Field of the Invention
This invention relates to wave-guiding structures and, more specifically, it relates to wave-guiding structures in which the lasing species is erbium, eg the ion Er.sup.3+. The lasing species is contained in a silica based glass.
2. Related Art
During the period 1985-1990 there has been substantial interest in the use of photonic amplifiers in telecommunications optical networks. This has included both semiconductor devices in which the primary source of power is electrical as well as wholly optical devices in which a signal at one optical wavelength is amplified and the power to drive the amplification is derived from a pump optical signal at a different frequency. The wholly optical devices can be configured in the form of a fibre wave-guide which is geometrically compatible with the transmission fibre in the telecommunications network. This geometrical compatibility confers substantial operating advantages and these advantages have given substantial technical significance to research into lasing structures and especially into lasing structures which can be implemented in the form of fibre.
Wavelengths in the range 1500 nm to 1600 nm have been recognised as particularly suitable for use in optical telecommunications and, therefore, photonic amplifiers which amplify at these wavelengths are of particular interest. It has been recognised that erbium, eg the ion Er.sup.3+, will, when suitably pumped, lase at these wavelengths. Thus photonic amplifiers based on erbium as a lasing species have been extensively studied.
More recently it has been recognised that erbium contained in a host glass of silica and germania has an operational bandwidth which is undesirably narrow for some applications. For example, it may be desired to operate a frequency division multiplex which uses optical signals at both 1530 nm and 1560 nm. It has been found difficult to achieve satisfactory amplification at both of these wavelengths because of the narrow operational bandwidth of the erbium lasing species.